1. Field of the Invention
The present invention relates to a marine vessel propulsion apparatus.
2. Description of the Related Art
A conventional marine vessel propulsion apparatus is described in, for example, U.S. Pat. No. 6,402,577. This marine vessel propulsion apparatus includes a transom bracket, a steering shaft, an outboard motor, a tilt mechanism, and a steering mechanism.
The transom bracket attachable to the transom of a hull is joined to the steering shaft. The steering shaft is turnable around a steering axis extending in the up-down direction with respect to the transom bracket. The outboard motor joined to the steering shaft is turnable around a tilt axis extending in the horizontal direction with respect to the steering shaft. The outboard motor and the steering shaft are turnable around the steering axis with respect to the transom bracket.
The tilt mechanism turns the outboard motor around the tilt axis with respect to the steering shaft. The steering mechanism turns the outboard motor and the steering shaft around the steering axis with respect to the transom bracket. The steering mechanism described in U.S. Pat. No. 6,402,577 is a hydraulic steering mechanism including a hydraulic pump. By driving the hydraulic pump, a hydraulic pressure is generated and this hydraulic pressure turns the outboard motor around the steering axis.
The steering mechanism described in U.S. Pat. No. 6,402,577 includes a steering arm and a steering actuator. The steering actuator includes a housing (a first portion of the steering actuator) and a rod (a second portion of the steering actuator). The housing and the rod extend in the right-left direction. The rod is disposed inside the housing. The housing has two cavities (hollows) disposed on the lateral sides of the right end portion and the left end portion of the rod. Hydraulic oil is supplied to these two cavities. The cavities are filled with the hydraulic oil. When a difference in hydraulic pressure is caused between the two cavities, the rod moves in the right-left direction inside the housing.
The rod is attached to the steering arm. The steering arm is attached to the outboard motor. When a difference in hydraulic pressure is caused between the two cavities and the rod moves in the right-left direction, the steering arm turns around the steering axis at a turning angle corresponding to a movement distance of the rod. When the steering arm further turns around the steering axis, the outboard motor turns around the steering axis together with the steering arm. Therefore, when the rod moves in the right-left direction, the outboard motor turns around the steering axis at a turning angle corresponding to the movement distance of the rod.